An integrated Hall effect sensor-based pump is known in the art, and may include an integrated pump motor and controller assembly. Such pumps are often employed in fields of facilities management and the like.
Referring to the prior art of the integrated pump motor and controller of FIG. 1, the BLDC motor rotor 6-102 and pump 6-104 are located on a common shaft 6-106, housed in a fluid filled housing 6-108. The BLDC motor stator and windings 6-110 are encased in a molded EPOXY body 6-112 that is located in the housing 6-108. The body 6-112 serves to seal the fluid in the housing 6-108 from the controller cavity 6-114. The BLDC motor controller circuit boards 6-116, 6-118 and 6-120 are supported in the controller cavity 6-114. A plurality of Hall effect sensors 6-122 are encased in the molded EPOXY body 6-112. The Hall effect sensors 6-122 are symmetrically arranged with respect to the axis of rotation of the rotor 6-102. Each sensor 6-122 is fitted and securely mounted within the molded EPOXY body 6-112 and appropriately positioned for measuring the angular position of the rotor. The sensors are wired together to generate a series of pulses (TACH signal) indicative of the speed of rotation. The operation of such sensors, as well as their application to the measurement of speed of rotation of a rotor within a switching electrical field, are well understood by those skilled in the art. Encasing the sensors within the body serves to protect the sensors from the fluid environment while allowing for correct position reading of the rotor magnets 6-124.
Current rotary position sensors, such as Hall effect sensors, are sensitive devices that often cannot be subjected to hydraulic fluid under pressure. It is therefore necessary to shield the rotary sensor from the hydraulic fluid pressure while not impeding its ability to accurately sense position. It is common practice to use three Hall effect sensors disposed radially around the axis of rotation of the motor rotor and a 4-pole ring magnet that is axially located after the rotor magnets. This arrangement may yield a resolution of about 30° and does not provide an absolute position. This may be an adequate resolution for certain applications, but to provide accurate control and responsiveness of a high speed, high precision application, such as an active suspension application in a vehicle, a much finer resolution is required. Although it is possible to use more than three Hall effect sensors disposed radially around the axis of rotation, there becomes a limit to how many can be located, due to their physical size, as well as other constraints such as cost and complexity of connecting many sensors to a controller, and the like. As such this method of position sensing becomes impractical for applications that require fine position sensing resolution and/or absolute position sensing, such as in the application of sensing rotor position for active suspension actuators.
Another drawback of the prior art described above is that in order for the Hall effect sensor(s) to accurately sense the position of the source magnet (or ring magnet) it is typical for the source magnet (or ring magnet) to protrude beyond the length of the stator and stator windings, so that magnetic flux from the rotor magnets and stator windings do not interfere the flux from the source magnet (or ring magnet) and hence disturb the Hall effect sensor(s). This has the effect of increasing the length and the inertia of the rotor in order to support the source magnet (or ring magnet). Certain applications of motor use (such as that of an active suspension actuator, whereby rapid motor accelerations and reversals are experienced), are very sensitive to the inertia of the motor rotor, and increasing the length (and hence inertia) of the rotor to accommodate the Hall effect sensors, without any increase of motor torque, may not be desirable in such applications.